Abstract: Ultra-structural changes in mesophll cells of two breeds of Chinese cabbage (“Wuyueman” and “Shanghaiqing”) under copper stress were investigated with transmission electron microscopy. When Chinese cabbage grows in the normal copper condition, various organelles of the crop morphologically integrate. But when it grows under copper stress, the number of chloroplasts reduces with increasing external copper concentration in both breeds. The chloroplast structure in leaf cells of “Wuyueman” is slightly injured when the concentration of Cu²⁺ reaches 10～20 mg·L-1. However, chloroplast membrane disrupts, some mitochondria cristae decreases, and certain crystal structure in some leaf mitochondria cells of “Wuyueman” are observed under high concentration of Cu²⁺(40～50 mg·L-1). In the leaf cells of “Shanghaiqing”, it is observed that ultrastructural damage gradually strengthens with increased Cu2+ concentration. The cell wall and cytoplast are separated, the chloroplast membrane is almost disorganized, some mitochondria cristae float in chaos and the vesicular sphere is visible under such concentration. The results also indicate that “Shanghaiqing” is more sensitive to copper stress than “Wuyueman”.